Voltage multiple dimming control apparatus

ABSTRACT

The present invention discloses a control apparatus, which not only accepts multiple dimming control signals, but also combines the signals in analog manner. By means of this, an inevitable analog to digital converter in a conventional voltage multiple dimming control apparatus can be saved without hurting the performance of generation of pulse width modulation signals. Compared with the conventional arts, the present invention further exhibits reduction in view of chip size and power consumption.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a voltage multiple dimming controlapparatus, more particularly to, a voltage multiple dimming controlapparatus for correctly generating pulse width modulation signalswithout using an analog to digital converter.

2. Description of the Prior Arts

Nowadays, LED plays a role of LCD backlight module, gradually, toreplace the CCFL backlight module. And the dimming characteristics ofthe backlight module can provide a better viewing and power consumptionsaving. Compared with CCFL, LED can offer better dimmingcharacteristics. Brightness for backlight, such as environmental lightsource sensing or color contents, for instance, can be manipulated indifferent approaches. Generally speaking, all of the various controlapproaches should be combined in order to reach an optimal value.

Refer to FIG. 1; a circuit diagram for conventional voltage multipledimming control apparatus is illustrated, for which two dimming controlsare included, and one of them is exhibited as pulse width modulationsignal input terminal 1 whilst another is exhibited as a digital signalinput 2. Furthermore, the conventional voltage multiple dimming controlapparatus further comprises an additional input 3 so as to control thedimming frequency of a pulse width modulation generator.

The aforesaid pulse width modulation signal passes a low-pass filterthus its high-frequency ripples are filtered and its DC signal will beconverted to a plurality of digital codes by an analog to digitalconverter 5.

The aforesaid digital codes should be digital in term of serial formator parallel format, which comprises a plurality of bits for signaldimming control. And the signal, overall speaking, will be used forfurther processing.

Also, two of the aforesaid dimming controls will be in process, and oneof the processes is to multiplication of the two controls in order toobtain the desirable dimming rate. Unfortunately, a digital multiplier 6will occupy a huge space and further consume a lot of power.Exemplarily, a multiplier characterized in 8 bits×8 bits, requires atleast 64 adders.

Accordingly, in view of the above drawbacks, it is an imperative that avoltage multiple dimming control apparatus is designed to generating apulse width modulation signal without the cost of an analog to digitalconverter so as to solve the drawbacks as the foregoing and to furtherreduce the circuit die size and power consumption.

SUMMARY OF THE INVENTION

In view of the disadvantages of prior art, the primary object of thepresent invention relates to a voltage multiple dimming controlapparatus, characterized in correct pulse width modulation without usingan analog to digital converter.

According to one aspect of the present invention, one skilled in the artcan come out a voltage multiple dimming control apparatus, comprising: apulse width modulating signal input terminal, for inputting a pulsewidth modulating signal; a digital signal input terminal, for inputtinga digital signal; a power signal to analog signal unit, for receivingthe pulse width modulating signal and converting the same into a firstanalog signal and a second analog signal, where the second analog signalis smaller than the first analog signal in their references; a digitalto analog unit, for receiving the digital signal and converting the sameinto a third analog signal and a fourth analog signal, where the fourthanalog signal is smaller than the third analog signal in theirreferences; a first multiplying unit, for multiplying the first analogsignal with the third analog signal so as to generate a first product; asecond multiplying unit, for multiplying the second analog signal withthe fourth analog signal so as to generate a second product; a voltageslope generating unit, for receiving a frequency setup signal togenerate a sloped voltage; and a judging unit, for generating anon-or-off signal or a reset signal based upon said sloped voltage, saidfirst product, and said second product, where the on-or-off signalOn/Off is used for turning on or turning off a dimming output, and saidreset signal is for resetting the voltage slope generating unit.

Hence, the present invention discloses an approach devoid of theconventional analog to digital converter, which an correctly generatepulse width modulating signal so that the whole circuit utilization diesize and the operating power can be further reduced.

Further scope of applicability of the present application will becomemore apparent from the detailed description given hereinafter. However,it should be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become readily understood from the detaileddescription given herein below and the accompanying drawings which aregiven by way of illustration only, and thus are not limitative of thepresent invention and wherein:

FIG. 1 relates to a circuit diagram of the conventional voltage multipledimming control apparatus;

FIG. 2 relates to a functional block diagram of a preferred embodimentaccording to the present invention; and

FIG. 3 relates to a circuit diagram of a preferred embodiment accordingto the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The following descriptions are of exemplary embodiments only, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the following description provides aconvenient illustration for implementing exemplary embodiments of theinvention. Various changes to the described embodiments may be made inthe function and arrangement of the elements described. For youresteemed members of reviewing committee to further understand andrecognize the fulfilled functions and structural characteristics of theinvention, several exemplary embodiments cooperating with detaileddescription are presented as the follows.

Turning up to FIG. 2 and FIG. 3, which illustrate a functional blockdiagram and a circuit diagram respectively as one of the preferredembodiments of the present invention. The present invention relates to avoltage multiple dimming control apparatus 7, comprises: a pulse widthmodulating signal input terminal 8, for inputting a pulse widthmodulating signal; a digital signal input terminal 9, for inputting adigital signal; a power signal to analog signal unit 10, for receivingthe pulse width modulating signal and converting the same into a firstanalog signal and a second analog signal, where the second analog signalis smaller than the first analog signal in their references; a digitalto analog unit 11, for receiving the digital signal and converting thesame into a third analog signal and a fourth analog signal, where thefourth analog signal is smaller than the third analog signal in theirreferences; a first multiplying unit 12, (such as an analog multiplier),for multiplying the first analog signal with the third analog signal soas to generate a first product; a second multiplying unit 13 (such as ananalog multiplier), for multiplying the second analog signal with thefourth analog signal so as to generate a second product; a voltage slopegenerating unit 14, for receiving a frequency setup signal 15 togenerate a sloped voltage Vramp; and a judging unit 16, for generatingan on-or-off signal On/Off or a reset signal based upon said slopedvoltage Vramp, said first product, and said second product, where theon-or-off signal On/Off is for turning on or turning off a dimmingoutput 17, said reset signal Reset is for resetting the voltage slopegenerating unit 14. Generally speaking, the judging unit 16 can becomposed of a first comparator 18 and a second comparator 19, whereinthe first comparator 18 is for comparing the second product and thesloped voltage Vramp to generate the on-or-off signal, and the secondcomparator 19 is for comparing the first product and the sloped voltageVramp to generate the Reset. The power signal to analog signal unit 10comprises: a CMOS 20, which includes a first terminal, a secondterminal, a third terminal, and a fourth terminal, wherein the thirdterminal is connected to ground; an inverter 21, having an inputterminal coupled to the pulse width modulating signal input terminal 8and having an output terminal coupled to the first terminal; an adjustor22, coupled to the second terminal, for adjusting the first analogsignal; and a low-pass filter 23, coupled to the fourth terminal, foroutputting the second analog signal.

As the follows, the first product and the second product are furtherillustrated in the preferred embodiment in the present invention,together with how to judge the time frame for generating the on-or-offsignal or the aforesaid Reset. Please refer to FIG. 2 and FIG. 3 again,the pulse width modulating signal will convert its duty cycle to be thesecond analog signal, whose maximum analog reference value is determinedby the first analog signal. Meanwhile, the digital signal is as wellconverted to be the fourth analog signal and the third analog signal,and the maximum analog reference value of the fourth analog signal isdetermined by the third analog signal. Afterwards, the second analogsignal is multiplied by the fourth analog signal so as to obtain thesecond product, and the first analog signal is multiplied by the thirdanalog signal so as to obtain the first product. After the aforesaidsecond product and first product are obtained, there will be acomparison between the sloped voltage Vramp and the first product/secondproduct. While the sloped voltage Vramp is smaller than the secondproduct, then the backlight will be turn on by said on-or-off signal(On). While the sloped voltage Vramp is larger than the second productbut smaller than the first product, then the backlight will be turn offby said on-or-off signal (Off). While the sloped voltage Vramp is largerthan the first product, then the Reset will be generated so as to enactthe whole judge flow to be re-circling. As illustrated by FIG. 3, thelow-pass filter 23 is composed of a resistor R1 and a capacitor C1 forfacilitate the conversion from the pulse width modulating signal to thesecond analog signal. The dimming frequency for the backlight can becontrolled by a variable resistor Rfreq that is used for generate anaccurate current Ifreq. Correspondingly, an accurate voltage isgenerated by a bandgap block 24, and their mutual relationship refersas: Ifreq=Vbg/Rfreq . . . (1)

The accurate current Ifreq will be mirrored and to charge a capacitorCramp so as to generate the sloped voltage Vramp. While the slopedvoltage Vramp is greater than the first product, the Vramp will berepeatedly and periodically reset so as to generate a periodic saw-toothwaveform, and its frequency can be expressed as Ifreq/(Cramp*the firstanalog signal*the third analog signal) . . . (2)

From the substitution between the equation (1) and the equation (2), theskilled artisan can have: its frequency can be also express as:Vbg/Rfreq*(Cramp*the first analog signal*the third analog signal).

Further in view of the dimming loading efficiency, that is, the secondproduct/the first product . . . (4) the skilled artisan can control thedesirable brightness.

From the aforesaid statement, the present invention can be clearlyunderstood as providing a voltage multiple dimming control apparatus,without using any analog to digital converter, which is still ablecapable of generating a pulse width modulating signal whilst the circuitdie size of the whole apparatus and power consumption can be reduced.

The invention being thus aforesaid, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A voltage multiple dimming control apparatus, comprising: a pulsewidth modulating signal input terminal, for inputting a pulse widthmodulating signal; a digital signal input terminal, for inputting adigital signal; a power signal to analog signal unit, for receiving thepulse width modulating signal and converting the same into a firstanalog signal and a second analog signal, where the second analog signalis smaller than the first analog signal in their references; a digitalto analog unit, for receiving the digital signal and converting the sameinto a third analog signal and a fourth analog signal, where the fourthanalog signal is smaller than the third analog signal in theirreferences; a first multiplying unit, for multiplying the first analogsignal with the third analog signal so as to generate a first product; asecond multiplying unit, for multiplying the second analog signal withthe fourth analog signal so as to generate a second product; a voltageslope generating unit, for receiving a frequency setup signal togenerate a sloped voltage; and a judging unit, for generating anon-or-off signal or a reset signal based upon said sloped voltage, saidfirst product, and said second product, where the on-or-off signalOn/Off is used for turning on or turning off a dimming output, and saidreset signal is for resetting the voltage slope generating unit.
 2. Thevoltage multiple dimming control apparatus as recited in claim 1,wherein said first multiplying unit is an analog multiplier.
 3. Thevoltage multiple dimming control apparatus as recited in claim 1,wherein said second multiplying unit is an analog multiplier.
 4. Thevoltage multiple dimming control apparatus as recited in claim 1,wherein said judging unit further comprises a first comparator forcomparing the second product and the sloped voltage to generate theon-or-off signal, and a second comparator for comparing the firstproduct and the sloped voltage to generate the reset signal.
 5. Thevoltage multiple dimming control apparatus as recited in claim 1,wherein said power signal to analog signal unit further comprises: aCMOS, including a first terminal, a second terminal, a third terminal,and a fourth terminal, wherein the third terminal is connected toground; an inverter, having an input terminal coupled to the pulse widthmodulating signal input terminal and having an output terminal coupledto the first terminal; an adjustor, coupled to the second terminal, foradjusting the first analog signal; and a low-pass filter, coupled to thefourth terminal, for outputting the second analog signal.